Over the past summer, the ALMR team has been conducting site upgrades on various sites throughout the state, mainly replacing the original Quantar repeaters with new GTR series repeaters.  This is a pre-requisite to an entire system upgrade, scheduled for next fall.  Throughout the winter and next summer, extensive work will be done on the system to complete the upgrade.  In addition to replacing repeaters, some sites have had new antennas and other equipment replaced as well, which should allow for improved system coverage.

The system upgrade will allow ALMR to switch the technology used for the system to TDMA – an acronym for Time Division Multiple Access.  This is a new way of using the radio frequency spectrum we have available to us that is significantly more efficient.  While that seems like an advantage for the system, what does that mean for users?  Essentially, that efficiency allows us double the amount of capacity in the system.  That means for each voice channel at a site, two users can utilize it at the same time.  Right now, only one user per voice channel is available.

ALMR is working with vendors to acceptance test various radios that have the TDMA capability.  This will allow options for all member agencies when it comes time to replace subscriber units.  As a reminder, policy does not allow any non-TDMA capable radio to be added to the system.  Agencies purchasing radio units should ensure they are capable of “TDMA Phase II.”   The approved equipment list shows which units have been designated as TDMA capable so far.

When the upgrade is completed in fall of 2022, we look forward to having upgraded equipment at each site with double the voice channel capacity of our current system, in addition to several new features that will become available with these updates.  Please don’t hesitate to reach out to the Help Desk or Operations Management Office with any questions.

Some of the additional features include:

P25 Phase II TDMA and Dynamic Dual Mode (DDM) at all State of Alaska sites.  The DDM feature allows a single channel to either operate in FDMA or TDMA mode depending on the affiliated talkgroup and user radio capabilities.  Dynamic Transcoding is also included, which enables efficient communication between FDMA and TDMA sites without downgrading the channel to its lowest common denominator, FDMA.  Although the included P25 infrastructure will support TDMA, to function it will also require TDMA subscribers.

With Dynamic Dual Mode (DDM), the voice channel is capable of either FDMA or TDMA, and the system will smart select based on the users on that talkgroup.  For DDM capable RF sites and subsystems, the system determines which mode is used to assign calls over-the-air in a dynamic manner.  The P25 site control channel and IV&D data continues to operate in FDMA mode.  From an end user perspective, FDMA and TDMA calls will operate the same.

Dynamic Dual Mode offers several advantages with the implementation of Phase 2 TDMA software:

  • Provides flexible migration to Phase 2 TDMA with support for both Phase 1 and Phase 2 TDMA user radios.
  • Ensures continued compatibility with neighboring Phase 1 systems and sites.
  • Minimizes system resources – other systems partition channels for exclusive operation in either the Phase 1 or Phase 2 mode which increases the number of base stations and frequencies necessary to operate the system effectively.

Dynamic Transcoding enables communication between FDMA and TDMA.  Because the call type is determined on a site-by-site basis, more sites can operate in TDMA – even in a mixed fleet of FDMA and TDMA radios.  This means you get a more efficient use of channels and frequencies, and all sites and radios can participate in a call regardless of the originating call type.  Dynamic transcoders reside in each zone core, translating between FDMA and TDMA audio formats.  Each site operates in the best mode based on the channel resources available and capabilities of the radios at that site.  Radio users communicate without a console patch or the need to downgrade the call.  Radio users from TDMA and FDMA-only sites are able to join a Dynamic Talkgroup without changing the call type at either site.

If all TDMA resources at a site are busy, the call can still go through because ASTRO 25 with transcoding will switch the call at that site to available FDMA resources, rather than wait for TDMA resources at that site to free up.  When TDMA resources are freed up, subsequent calls will switch back to TDMA at that site so you gain higher efficiencies.


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